Lesson 35 · Unknown names and bad references

Unknown names and bad references

Two more errors complete the set - calling a function that does not exist, and using a reference where it makes no sense. Today you add

The goal

Return

Start here - the target

TO DO

Scenario: Bad names and misused references error

Givenformulas that call an unknown function or misuse a range

Whenthey are evaluated

Theneval('=FOO(1)') is the Error '#NAME?' since FOO is not a known function

Andeval('=A1:A3') is the Error '#REF!' - a bare range is not a single value - and eval('=1+A1:A3') is '#REF!' as well

Background

Two final error kinds round out the set. #NAME? is what the evaluator returns when a CallNode names a function it does not recognize - the default case of the function dispatch. Type =FOO(1) and, since FOO is not one of the six functions, the cell shows #NAME? rather than silently returning nothing. #REF! covers a bad reference: a range like A1:A3 is only meaningful inside a function that expects one (like SUM), so using it as a plain value - =A1:A3, or =1+A1:A3 - is a reference error.

Both new errors flow through the propagation rule from the last lesson: a cell that reads a #NAME? cell becomes #NAME?, and a SUM over a range holding an error is that error. The engine now has the full family - #CIRC! for cycles, #DIV/0! for division, #NAME? for unknown functions, #REF! for bad references - and every one of them spreads correctly downstream. With errors handled, the last piece of the core is making an ordinary edit trigger a recalculation automatically.

Make it work

// in evalCall, the default case (no matching function name):
default:
  return Value{Kind: Err, Code: "#NAME?"}
// evaluating a RangeNode outside a function argument:
case RangeNode:
  return Value{Kind: Err, Code: "#REF!"} // a range is not a scalar

CheckpointDONE

Unknown functions and misused ranges now error cleanly. Commit and stop here.